Hydrocarbon lube and distillate fuel additive

ABSTRACT

A hydrocarbon oligomer and a process for its production is disclosed that is useful as a pour point depressant and as a combination pour point depressant and viscosity index improver for mineral oil or synthetic oil. The oligomer is also useful in modifying wax crystal formation at low temperature when added to distillate fuels. The oligomer is a near linear copolymer of a mixture of ethylene and C 3  -C 28  1-alkenes, or only 1-alkenes, wherein a large proportion of the pendant alkyl groups of the recurring 1-alkene monomer units contain between 14 and 22 carbon atoms. The oligomer is produced by polymerization of mixed 1-alkenes with reduced chromium oxide catalyst on silica support.

This invention relates to novel additives for hydrocarbon lubricants anddistillate fuels and to the process for their production. The inventionparticularly relates to novel hydrocarbon additives useful as pour pointdepressants and additives which show combined pour point depressant andviscosity index improving properties for hydrocarbon lubricants andinhibitors of waxy particle formation in diesel fuel at lowtemperatures. The novel additives are produced by reduced chromium oxidecatalyzed polymerization of mixed 1-alkenes rich in C₁₈ + 1-alkenes.

BACKGROUND OF THE INVENTION

The formulation of synthetic or mineral oil based lubricants typicallyincludes an additive package incorporating a variety of chemicals toimprove or protect lubricant properties in application specificsituations, particularly internal combustion engine and machineryapplications. The more commonly used additives include oxidationinhibitors, rust inhibitors, antiwear agents, pour point depressants,detergent-dispersants, viscosity index (VI) improvers, foam inhibitorsand the like. This aspect of the lubricant arts is specificallydescribed in Kirk-Othmer "Encyclopedia of Chemical Technology", 3rdedition, Vol. 14, pp 477-526, incorporated herein by reference. Theinclusion of additives in hydrocarbon lubricants provides a continuingchallenge to workers in the field to develop improved additives ofincreased compatibility with the lubricant. Superior additives, whilecontributing their inherent attribute to the formulation, must do sowhile maintaining or improving upon the composite thermal and oxidativestability of the lubricant formulation.

The low temperature flow characteristic of hydrocarbon lubricants aretypically improved by adding pour point depressants (PPD) to theformulation. At low temperatures, these additives modify the shape andsize of the precipitating waxy hydrocarbon crystal to slow agglomerationand lower the effective pour point temperature of the lubricantformulation. Currently, preferred pour point depressants includepolymethacrylares and ethylene-vinyl ester polymers. However,hydrocarbon based pour point depressants are known.

Polyalphaolefin (PAO) pour point depressants are described byChong-Xiang Xiong in "The Structure and Activity of Polyalphaolefins asPour Point Depressants", published in the Journal of the Society ofTribologists and Lubrication Engineers, March, 1993, pp 196-200. The PPDis prepared by polymerization of slack wax-derived C₇ -C₂₀ alphaolefinsusing Ziegler-Natta catalyst. It is reported that PAO pour pointdepressant activity depends on average side chain length and on thedistribution of the side chain length. Base oil characteristicsinfluence the effectiveness of specific PAO pour point depressants.

It is also known that the low temperature flow properties of waxydistillate fuels can be improved by employing wax crystal modifiers asadditives to fuels in a manner functionally similar to waxy lube PPD.The use of such additives to distillate fuels avoids the more costlystep of deep dewaxing of the distillate feedstock.

One class of lubricants of particular interest in the present inventionis synthetic lubricants obtained by the oligomerization of olefins,particularly C₃ -C₂₀ alpha olefins. Catalytic oligomerization of olefinshas been studied extensively. Known olefin oligomerization catalystsinclude the Ziegler-Natta type catalysts and promoted catalysts such asBF₃ or AlCl₃ catalysts. U.S. Pat. No. 4,613,712 for example, teaches thepreparation of isotactic alpha-olefins in the presence of a Ziegler typecatalyst. Other coordination catalysts, especially chromium on a silicasupport, are described in the art.

Recently, novel lubricant compositions (referred to herein as HVI-PAOand the HVI-PAO process) comprising polyalphaolefins and methods fortheir preparation employing as catalyst reduced chromium on a silicasupport have been disclosed in U.S. Pat Nos. 4,827,064 and 4,827,023,incorporated herein by reference in their entirety. The processcomprises contacting C₆ -C₂₀ 1-alkene feedstock with reduced valencestate chromium oxide catalyst on porous silica support underoligomerizing conditions in an oligomerization zone whereby highviscosity, high VI liquid hydrocarbon lubricant is produced having lowmethyl to methylene branch ratios of less than 0.19 and pour point below-15° C. The process is distinctive in that little isomerization of theolefinic bond occurs compared to known oligomerization methods toproduce polyalphaolefins using Lewis acid catalyst.

U.S. Pat. No. 5,146,021 to Jackson, et al. discloses lube compositionsof HVI-PAO with mineral oil and polyolefins wherein oligomers frommixtures of C₆ -C₂₀ alphaolefins are employed to provide high VIadditives and shear stability. However, the patent does not claim ordisclose the use of mixtures containing a high proportion of C₁₈ + alphaolefins to produce improved pour point depressants. U.S. Pat. No.5,157,177 to Pelrine et al. discloses the oligomerization processrelevant to the preparation of the foregoing HVI-PAO compositions. Thecompositions and process disclosed in these patents encompass polymercompositions that contain non-waxy components. The polymers are usefulas lubricants with low pour point.

The object of the present invention is the production of novel lubricantadditive hydrocarbon compositions that are highly effective as pourpoint depressants and/or combined pour point depressant and viscosityindex improver (VII) produced by catalytic oligomerization of 1-alkenes.

Another object of the present invention is to provide an improvedprocess for the production of pour point depressants by oligomerizationof 1-alkenes using silica supported reduced chromium oxide catalyst.

Yet another object of the invention is to provide a pure hydrocarbonadditive for distillate fuels that is effective in modifying wax crystalgrowth at low temperatures.

SUMMARY OF THE INVENTION

Hydrocarbon oligomers, and a process for their production, have beendiscovered that show superior properties as pour point depressants formineral oil or synthetic oil. The oligomers are also useful in modifyingwax crystal formation at low temperature when added to distillate fuels.The oligomer is a near linear copolymer of a mixture of ethylene and C₃-C₂₂ 1-alkenes, or only 1-alkenes, wherein a large proportion of thependant alkyl groups of the recurring 1-alkene monomer units containbetween 12 and 22 carbon atoms, preferably between 14 and 18 carbonatoms. The linearity of the 1-alkene copolymer is distinguished by therelatively small amount of isomerization that occurs duringcopolymerization by the process disclosed in U.S. Pat Nos. 4,827,064 and4,827,023 and evinced by a methyl to methylene branch ratio of less than0.19 for oligomers formed from C₆ + 1-alkenes.

The superior pour point depressant properties of the compositions of theinvention are preferably achieved by preparing oligomers from afeedstream mixture of ethylene and C₃ -C₂₈ 1-alkenes, or only C₃ -C₂₈1-alkenes, wherein the distribution of carbon numbers is bimodal insteadof monomodal. Bimodal distribution in the present invention means thatcarbon number distribution in the total feedstream is skewed in such amanner as to exhibit two peaks, one peak of low carbon number andanother peak of high carbon number. The bimodal feedstream produces thebimodal 1-alkene copolymers of the present invention comprisingcopolymers having a first maximum of pendant carbon chains with betweenone and 12 carbon atoms and a second maximum of pendant carbon chainswith between twelve and twenty-four carbon atoms.

In comparison to pour point depressants known in the art, the novelhydrocarbon oligomers of the invention show a dramatic capability toreduce the low temperature pour point of mineral oils and synthetic oilswhen mixed with such liquids in quantities of less than 1 weightpercent. When mixed with diesel fuels containing hydrocarbons thatnormally form wax crystals at low temperature, the oligomers of theinvention modify the formation of wax crystals and minimize waxformation in the fuel.

As VI improvers, these novel hydrocarbon oligomers work as effectivelyas the single olefin based HVI-PAO's disclosed in U.S. Pat. No.5,146,021. In addition, they add pour point depressant function to theVI improver. The novel oligomers of the invention are cited herein asmixed alpha-olefin HVI-PAO, or MHVI-PAO, to distinguish them over theHVI-PAO oligomers of the prior art.

The products of the invention are prepared by oligomerizing olefins,preferably a mixture of C₆ -C₂₄ 1-alkenes containing at least 10 weightpercent of C₁₄ -C₂₄ 1-alkenes, preferably C₁₆ -C₂₀ 1-alkenes, in contactwith supported reduced valence state chromium oxide catalyst.

More particularly, a hydrocarbon lubricant additive has been discoveredthat is suitable as a pour point depressant. The additive comprises thecopolymer residue of a mixture of 1-alkene comonomers selected from thegroup consisting of C₃ -C₂₈ 1-alkenes. The copolymer contains at least10 weight percent of C₁₄ -C₂₄ 1-alkenes, but preferably 20 weightpercent. It also has a number average molecular weight between 5,000 and60,000; and a molecular weight distribution between 1 and 10.

The product of the invention is a near-linear liquid hydrocarboncopolymer useful in modifying the low temperature formation of waxparticles in liquid hydrocarbon lubricants and fuels. The copolymercomprises poly(1-alkene) having a low methyl to methylene branch ratioand containing between 300 and 4500 carbon atoms, wherein recurringmonomeric units of said copolymer comprise a mixture of ethylene and C₃-C₂₈ 1-alkene, or C₃ -C₂₈ 1-alkenes, and at least 10 weight percent ofthe pendant chains of said copolymer contain between 12 and 22 carbonatoms, most preferred pendant chains are C₁₄ to C₁₈.

The product of the invention is prepared by contacting a mixture ofolefin comonomers selected from the group consisting of ethylene and C₃-C₂₈ 1-alkenes with a reduced valence state Group VIB metal catalyst ona porous support under copolymerization conditions. The mixture containsat least 10 weight percent of C₁₄ -C₂₄ 1-alkenes, preferably C₁₆ -C₂₀1-alkenes. The product of the copolymerization is separated and acopolymer comprising the additive is recovered.

DESCRIPTION OF THE FIGURES

FIG. 1 is a graphical representation comparing the feed composition ofHVI-PAO versus the novel MHVI-PAO oligomers of the invention.

FIG. 2 is a graphical representation of the feed composition of HVI-PAOof the prior art.

FIG. 3 is a graphical representation of the feed composition of onepreferred embodiment of MHVI-PAO of the invention.

FIG. 4 is a graphical representation of the feed composition of anotherpreferred embodiment of MHVI-PAO of the invention.

FIG. 5 is a graphical representation of the feed composition of yetanother preferred embodiment of MHVI-PAO of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Olefins useful as feedstock in the present invention include ethyleneand C₃ -C₂₈ 1-alkenes of odd and even carbon number. The preferredolefins are 1-alkenes, i.e., alpha-olefins selected from the groupconsisting of C₆ -C₂₄ 1-alkenes. The preferred long chain 1-alkenescomprise C₁₄ -C₂₄ α-olefins. The most preferred long chain 1-alkenescomprise C₁₆ -C₂₀ α-olefins.

A feature inherent to the novelty of the instant invention is that thefeedstock include a mixture of 1-alkenes and that the mixture of1-alkenes comprise at least 10 weight percent C₁₆ -C₂₄ 1-alkenes. Themixture may be a mixture of only two such 1-alkenes, for example,1-hexene and 1-octadecene, 1-decene and 1-eicosene, or it may be amixture that includes propylene, 1-butene, 1-pentene, 1-hexene,1-heptene, 1-octene, 1-nonene, 1-decene, and higher 1-alkenes up to andincluding C₂₈ 1-alkene. In any event, at least 10 weight percent, butpreferably 20 weight percent, of the 1-alkenes of the mixture will be1-alkenes containing 16 to 24 carbon atoms.

The feedstock for the process of the invention can be acquired from avariety of processes and process streams common to modern petroleumrefining operations. The products of slack wax cracking, ethylene growthreaction and Fischer-Tropsch alpha olefin process are useful sources ofmixed 1-alkenes. These and other sources of feed-stock may containalkanes and internal olefins. As a result, the 1-alkene feedstream tothe process of the invention itself may contain these alkanes andinternal olefins. However, these are not reactive in the oligomerizationreaction of the invention.

The oligomerization reactions of the invention are catalyzed bysupported metal oxide catalysts, such as Cr compounds on silica or othersupported IUPAC Periodic Table Group VIB compounds as described in U.S.Pat. No. 4,827,064 to M. Wu. The catalyst most preferred is a lowervalence Group VIB metal oxide on an inert support. Preferred supportsinclude silica, alumina, titania, silica alumina, magnesia and the like.The support material binds the metal oxide catalyst. These pouroussupports may be in powder form or in extrudate form. Those poroussubstrates having a pore opening of at least 40 angstroms are preferred.

The support material usually has high surface area and large porevolumes with average pore size of 40 to about 350 angstroms. The highsurface area are beneficial for supporting a large amount of highlydispersive, active chromium metal centers and to give maximum efficiencyof metal usage, resulting in very high activity catalyst. The supportshould have large average pore openings of at least 40 angstroms, withan average pore opening of >60 to 300 angstroms preferred. For thiscatalyst to be used in fixed bed or slurry reactor and to be recycledand regenerated many times, a silica support with good physical strengthis preferred to prevent catalyst particle attrition or disintegrationduring handling or reaction.

The supported metal oxide catalysts are preferably prepared byimpregnating metal salts in water or organic solvents onto the support.Any suitable organic solvent known to the art may be used, for example,ethanol, methanol, or acetic acid. The solid catalyst precursor is thendried and calcined at 200° to 900° C. by air or other oxygen-containinggas. Thereafter the catalyst is reduced by any of several various andwell known reducing agents such as, for example, CO, H₂, NH₃, H₂ S, CS₂,CH₃ SCH₃, CH₃ SSCH₃, metal alkyl containing compounds such as R₃ Al, R₃B,R₂ Mg, RLi, R₂ Zn, where R is alkyl, alkoxy, aryl and the like.Preferred are CO or H₂, CO or H₂ containing gas or metal alkylcontaining compounds.

Alternatively, the Group VIB metal may be applied to the substrate inreduced form, such as CrII compounds. The catalyst can be used in abatch type reactor or in a fixed bed, continuous-flow reactor.

In general the support material may be added to a solution of the metalcompounds, e.g., acetates or nitrates, etc., and the mixture is thenmixed and dried at room temperature. The dry solid gel is purged atsuccessively higher temperatures to about 600° for a period of about 16to 20 hours. Thereafter the catalyst is cooled down under an inertatmosphere to a temperature of about 250° to 450° C. and a stream ofpure reducing agent is contacted therewith for a period when enough COhas passed through to reduce the catalyst as indicated by a distinctcolor change from bright orange to pale blue. Typically, the catalyst istreated with an amount of CO equivalent to a two-fold stoichiometricexcess to reduce the catalyst to a lower valence CrII state. Finally thecatalyst is cooled down to room temperature and is ready for use.

Example 1 specifically illustrates the method for preparation of thecatalyst employed in the present invention and disclosed in U.S. Pat.No. 4,827,064.

EXAMPLE 1 Catalyst Preparation and Activation Procedure

1.9 grams of chromium (II) acetate (Cr₂ (OCOCH₃)₄ 2H₂ O)(5.58 mmole)(commercially obtained) is dissolved in 50 cc of hot acetic acid. Then50 grams of a silica gel of 8-12 mesh size, a surface area of 300 m² /g,and a pore volume of 1 cc/g, also is added. Most of the solution isabsorbed by the silica gel. The final mixture is mixed for half an houron a rotavap at room temperature and dried in an open-dish at roomtemperature. First, the dry solid (20 g) is purged with N₂ at 250° C. ina tube furnace. The furnace temperature is then raised to 400° C. for 2hours. The temperature is then set at 600° C. with dry air purging for16 hours. At this time the catalyst is cooled down under N₂ to atemperature of 300° C. Then a stream of pure CO (99.99% from Matheson)is introduced for one hour. Finally, the catalyst is cooled down to roomtemperature under N₂ and is ready for use.

While providing oligomers having a very low branch ratio, theoligomerization of 1-alkenes with reduced chromium oxide catalyst onsilica support also provides a highly uniform structural composition,particularly when compared to conventional polyalphaolefins produced byBF₃, AlCl₃ or Ziegler-type catalysis. HVI-PAO oligomers have been shownto have a very uniform linear side chain branch and contain regularhead-to-tail connections. The oligomers are essentially linear. Inaddition to the structures from the regular head-to-tail connections,the backbone structures have some head-to-head connections.

It has been discovered that activated reduced chromium catalyst on SiO₂support efficiently produces polymers with the right molecular weightrange and chemical composition to form useful additives from widemixtures of alphaolefins. The mixed olefin based HVI-PAO polymers show avery large pour point depressant effect when blended with wax containinglubricant basestocks. This result is evident while the mixed olefinbased polymers also are effective as viscosity index improvers (VII).The mixed olefin based HVI-PAO produced from reduced chromium catalyston SiO₂ support can also minimize wax formation when blended with dieselfuel. Thus, it can be used to improve the flow properties of waxy fuelsat low temperature. Since HVI-PAO polymers are pure hydrocarbons theywill have better thermal stability, oxidative stability and solubilityin hydrocarbon lubricants and distillate fuels then commercial pourpoint depressants or wax crystallization modifiers. These commercialadditives are mostly polymethacrylates or ethylene-vinyl estercopolymers.

Examples of specific lubricant base stocks for which the polymers of theinvention are effective as pour point depressants are summarized asfollows and their physical properties are presented in Table 1:

LN142-100", solvent neutral mineral base stock, available from Mobil OilCorp. as product number 71326-3, produced by methyl ethyl ketone solventdewaxing;

LN321-150", solvent neutral mineral base stock, produced by catalyticdewaxing;

HN339-700", heavy neutral mineral base stock, produced by catalyticdewaxing;

BS345 - bright stock mineral oil, produced by catalytic dewaxing;

WHI-A, WHI-B stocks - derived from slack wax. The wax is hydroisomerizedat high pressure, such as 1500-3000 psi over an amorphous catalyst orzeolite.

PAO-1, a 2 cS synthetic hydrocarbon poly-alpha-olefin fluid availablefrom Mobil Chemical.

PAO-2, a 5.5 cS synthetic hydrocarbon poly-alpha-olefin fluid availablefrom Mobil Chemical.

                  TABLE 1                                                         ______________________________________                                        Base Stock Properties                                                         Stock              Viscosity,                                                                             cS          Pour                                  No.    Stock Type  100° C.                                                                         40° C.                                                                       VI    Point °C.                      ______________________________________                                        LN142  mineral,    4.19     21.23 97    -14                                          solvent dewax                                                          LN321  mineral     4.61     24.1  106   -3                                           catalytic dewax                                                        HN339  mineral     13.08    138.53                                                                              86    -12                                          catalytic dewax                                                        BS345  mineral     30.2     460.62                                                                              94    4                                            catalytic dewax                                                        WHI-A  wax-isomerized,                                                                           5.35     26.1  144   -16                                          solvent dewax                                                          WHI-B  wax-isomerized,                                                                           5.14     24.16 148   -15                                          solvent dewax                                                          ______________________________________                                    

As noted, the products of the invention are useful in modifying waxformation in distillate fuels. Generally, distillate fuels include jetfuels, diesel fuels and heating oils. The compositions of the presentinvention are particularly useful in automotive and railroad dieselfuels.

The process and compositions of the present invention are described byillustrating their preparation and properties in the following Examples2-11. The Examples include the method for the preparation of the novelpolymers of the invention (Example 2) and the properties of blends ofthe novel polymers with various lubricant basestock (Examples 3-10) andwith diesel fuel (Example 11). The catalyst used in the oligomerizationof the mixed 1-alkene monomers is prepared according to the methoddescribed in Example 1. The results are shown in Table 2 for thepreparation of the copolymer of the invention and Table 3 shows theproperties of blends prepared from the copolymer with mineral oil andsynthetic lubricants (Examples 2-9).

EXAMPLE 2

Six grams of Cr/SiO₂ catalyst prepared as described in Example 1 weremixed with an alpha olefin mixture containing six to twenty carbonnumbers and the mixture was stirred at room temperature for twenty-fourhours. The alpha olefin mixture has a composition comparable to thealpha olefin mixture produced from a single stage ethylene growthreaction and is reported in Table 2. Gas chromatograph (GC) analysis ofthe polymer solution produced from the oligomerization reaction ofalphaolefins showed that 70% to 90% of the alpha olefins were convertedinto polymers. The slurry mixture was very thick and 400 cc of xylenewas added to dilute and quench the catalyst. The mixed olefin basedHVI-PAO polymer was isolated by filtration to remove the catalyst,followed by distillation at 160° C. and 100 millitorr to remove solventand any unreacted olefins. As shown in Table 1, the polymer compositioncontained different amounts of alphaolefins. All of the alphaolefins inthe starting mixture were converted into polymer. The residual olefinswere internal or branched olefins present in the starting mixture. Thispolymer had a number average molecular weight of 18,200, weight averagemolecular weight of 58,000 and molecular weight distribution of 3.19.

EXAMPLE 3

The sample prepared in Example 2 was blended with a light neutralparaffinic mineral base stock, LN321, which was dewaxed using acatalytic dewaxing process. The properties of the base stock and theblends are summarized in Table 3. These data show that the blendcontaining 0.26 weight percent of the product of Example 2 has a pourpoint of -38° C. and cloud point of 3.0° C., a 35° C. pour pointreduction and 2.6° C. cloud point reduction compared to the startingbase stock LN321. also the blend had higher VI than the base stock,i.e., 111 versus 106 for the base stock.

                  TABLE 2                                                         ______________________________________                                        Composition of Starting Olefin Mixtures and Polymers                          Carbon Olefin  Wt %    Wt % after                                                                            Conversion                                                                            % Olefin in                            Number MW      in Mix. 24 hrs  %       Polymer                                ______________________________________                                         6      84     6.8     1.9     72      6                                       8     112     9.4     0.8     91      11                                     10     140     13.3    1.2     91      15                                     12     168     11.1    1.1     90      12                                     14     196     11.8    3.1     74      11                                     15     210     7.5     1.7     77      7                                      16     224     7.6     1.2     84      8                                      18     252     6.2     1.6     74      6                                      20     280     25.6    6.8     73      23                                      20+   282     0.7     0.4     43      0                                      Polymer                                                                              --      0       80      --      --                                     ______________________________________                                    

EXAMPLE 4

The same base stock used in Example 3 was blended with a commercial VIimprover, Acryloid 956 (Example 4A), or commercial pour point depressantAcryloid 156 (Example 4C, and NALCO 5644 (Example 4B). The pour pointsof the blends were decreased only 2° to 26° C. and the cloud pointsremained the same as the base stock as shown in Table 3.

EXAMPLE 5

The product of Example 2 was blended with a mineral oil (LN142) whichwas prepared using a conventional solvent dewaxing process. Theproperties of the base stock and blends are summarized in Table 3. Thesedata show that the blend containing 0.49 weight percent of the productof Example 2 had a pour point of -37° C. and cloud point of -12.9° C.This corresponds to a 23° C. pour point reduction and 3.5° C. cloudpoint reduction compared to the starting base stock. Also, the blend hashigher VI than the base stock, 109 versus 97 for the stock.

EXAMPLE 6

A blend was prepared as described in Example 3, except the base stockwas a heavy neutral mineral basestock HN339. The pour point of HN339 wasdepressed from -12° C. to -27° when 0.26 weight percent of the productof Example 2 was blended.

EXAMPLE 7

A blend was prepared as described in Example 3, except the base stockwas mineral bright stock BS345. The pour point of BS 345 was depressedfrom +4° C. to -12° C. when 0.55 weight percent of the product ofExample 2 was added.

EXAMPLE 8

A blend was prepared as described in Example 3, except the base stockwas prepared from a wax hydroisomerization process. In this case, thepour point was depressed from -15° C. to -23° C.

                                      TABLE 3                                     __________________________________________________________________________    Example                                                                              Base oil                                                                           VII/PPD                                                                              Wt %  Pour V @ 40° C.,                                                                   V @ 100° C.,                                                                     Cloud                          No.    Type type   VII/PPD                                                                             point, °C.                                                                  cS     cS     VI Point °C.               __________________________________________________________________________    No. 3  LN321                                                                              none   0     -3   24.1   4.61   106                                                                              5.6                            "      "    Exam. 2                                                                              0.26  -38  24.81  4.74   111                               "      "    "      0.58  -28  25.87  4.94   116                                                                              1.5                            No.4                                                                          comparative                                                                   4A     "    Acryloid 956                                                                         0.25  -5   24.47  4.71   111                                                                              6.2                            4B     "    Nalco-5644                                                                           0.26  -26  24.15  4.63   107                                                                              na                             4C     "    Acryloid 156                                                                         0.24  -29  24.38  4.71   112                                                                              na                             No. 5  LN142                                                                              none   0     -14  21.32  4.19   97                                "      "    Exam. 2                                                                              0.49  -37  22.28  4.43   109                                                                              -12.9                          "      "    "      1.05  -32  23.94  4.71   115                                                                              -14.0                          No. 6  HN339                                                                              none   0     -12  138.53 13.08  86 na                             "      "    Exam. 2                                                                              0.26  -27  140.53 13.45  89 na                             "      "    "      0.5   -29  143.35 13.68  90 na                             No. 7  BS345                                                                              none   0     4    460.62 30.2   94 na                             "      "    Exam. 2                                                                              0.55  -12  468.05 30.78  95 na                             "      "    "      1.09  -14  486.05 32.91  100                                                                              na                             No. 8  WHI-A                                                                              none   0     -16  26.1   5.35   144                                                                              Na                             "      "    Exam. 2                                                                              0.65  -20  29.21  5.78   144                                                                              Na                             "      "    "      1.31  -18  30.22  6.13   157                                                                              Na                             No. 9  PAO-1                                                                              none   0     -66  5.2    1.7    90 na                             "      "    Exam. 2                                                                              0.51  -78  5.47   1.82   106                                                                              na                             "      "    "      1.73  -69  6.39   2.13   144                                                                              na                             No. 10 PAO-2                                                                              none   0     -62  30.5   5.5    135                                                                              na                             "      "    Exam. 2                                                                              0.45  -71  30.95  5.95   141                                                                              na                             "      "    "      1     -64  32.68  6.22   142                                                                              na                             __________________________________________________________________________

EXAMPLE 9

A blend was prepared as described in Example 3, except the base stockwas a low viscosity polyalphaolefin product of 1.7 cS. A 12° C. pourpoint reduction was observed.

EXAMPLE 10

A blend was prepared as described in Example 3, except the base stockwas a synthetic PAO base stock of 5.6 cS (stock 509). The pour pointreduction was 9° C.

EXAMPLE 11

A series of blends was prepared using a Coryton diesel fuel having apour point of -13.3° C. and a cloud point of -2.9° C. and the HVI-PAOproduct of Example 2. Pour points and cloud points were measured on theblends of these mixed HVIPAO oligomers with the diesel fuel and theresults are presented in Table 4. It was found that the mixed HVI-PAO isat least comparable to commercial fuel pour point depressants. However,the mixed HVI-PAO had extra cloud point depression which is not observedwith the commercial pour point depressants.

                  TABLE 4                                                         ______________________________________                                        HVI-PAO   Pour Point                                                                              Cloud Point                                               ppm       °C.                                                                              °C.   ΔPP                                                                          ΔCP                               ______________________________________                                        100       -31       -6.3         17.7 3.4                                     200       -26.5     -5.8         13.2 2.9                                     500       -28.7     -6.8         15.4 3.9                                     ______________________________________                                    

EXAMPLE 12

A two component HVI-PAO was prepared according to the general proceduredescribed in Example 2. The components were 1-decene and 1-octadecene.Oligomers were prepared from feeds containing 7% 1-octadecene, 25%1-octadecene and 40% 1-octadecene. When blends were prepared of mineraloil (LN321) containing the HVI-PAO oligomers, the corresponding pourpoint depression was -30° C. for 40% 1-octadecene, -13° C. for 25%1-octadecene and -7° C. for 7% 1-octadecene.

The amount of pour point depression depends on the concentration ofmixed HVI-PAO in the blend. The optimum concentration for the largestpour point depression is about 0.1 weight percent to about 0.4 weightpercent. Usually the best results are achieved using 0.20-0.30 weightpercent, preferably 0.25 weight percent. Above or below thisconcentration the amount of depression decreases. However, even at lowconcentrations in the range of 50-100 ppm a 5°-12° C. pour pointdepression is observed.

The HVI-PAO oligomers effective as pour point depressants in the presentinvention comprise copolymers of C₃ -C₂₈ 1-alkenes. The copolymercontains at least 10 weight percent of C₁₄ -C₂₄ 1-alkenes; has a numberaverage molecular weight between 5,000 and 60,000; a molecular weightdistribution between 1 and 10.

An important part of the novelty of the present invention resides in thediscovery that the copolymerization of certain mixtures of α-olefinsaccording to the process of the invention leads to oligomers of uniquestructure (MHVI-PAO) with unexpectedly superior properties as pour pointdepressants and, even more notable, combined pour point depressants andviscosity index improves. The novel oligomers are produced from mixedα-olefin feedstock having a bimodal distribution of carbon numbers forthe α-olefins. The distribution is such that the carbon numbers reachone maximum at a relatively high carbon number and another or secondmaximum at a relatively low carbon number. The preferred oligomers ofthe invention are characterized by exhibiting both maxima. This bimodalfeedstream leads to the formation of oligomers of the present inventioncomprising copolymers having a first maximum of pendant carbon chainswith between one and twelve carbon atoms and a second maximum of pendantcarbon chains with between twelve and twenty-four carbon atoms. In termsof 1-alkene content, the oligomer or coploymer residue contains recuringunits comprising a bimodal distribution of 1-alkenes having a firstmaximum between C₃ and C₁₄ 1-alkenes and a second maximum between C₁₄and C₂₆ 1-alkenes.

Referring to FIG. 1, a graphical representation is presented comparingthe feed composition of HVI-PAO versus the novel MHVI-PAO oligomers ofthe invention. The graph shows that the prior art HVI-PAO oligomersemploy monomodal feed mixtures having a single maximum of relatively lowα-olefin carbon number. Feeds for other MHVI-PAO oligomers of theinvention are also presented as bimodal. The distinction is emphasizedby referring to FIG. 2 which shows the monomodal feed composition usedfor prior art HVI-PAO synthesis. FIGS. 3-5 illustrate MHVI-PAO feedcompositions for particularly preferred oligomers of the inventionprepared from two or more α-olefins. Regardless of the mix, FIGS. 3-5show the uniquely bimodal distribution of olefins in the MHVI-PAOfeedstream with one maximum of six to ten carbon atoms and a secondmaximum falling between sixteen and twenty carbon atoms. Notably, therequired bimodal character of the feed does not preclude a continuum inα-olefin carbon numbers in the feed. This is illustrated in FIG. 4.

As noted herein before, liquid hydrocarbon polymers and copolymers ofalpha olefins (HVI-PAO) have been prepared by reduced chromium oxideoligomerization as disclosed particularly in U.S. Pat. No. 4,827,064 toM. Wu. These lubricant range oligomers exhibit unexpectedly highviscosity indices and low pour points. While these polymers arecompositionally different than the polymers of the present invention,their similarity is sufficient to provide a basis to conjecture that the(HVI-PAO) compositions of U.S. Pat. No. 4,827,064 would also beeffective pour points depressants. Accordingly, a series of experimentswere carried out (Examples 13-16) to compare the pour point depressantproperties of the HVI-PAO compositions of U.S. Pat. No. 4,827,064 withthe products of the instant invention.

In Examples 13-16, using 1-decene or C₆ -C₁₄ alpha olefins, HVI-PAOoligomers were prepared according to the above cited patent and thepolymer or copolymer product blended with Stock 142 mineral oil. Theresults of these experiments are presented in Table 5. The results showthat the HVI-PAO containing no C₁₆ or higher α-olefins produced no pourpoint depressant effect with Stock 142 mineral oil. Consequently, theproducts of the present invention are distinguished over those of otherHVI-PAO patents such as U.S. Pat. No. 4,827,064.

                  TABLE 5                                                         ______________________________________                                                  Blend Properties                                                    Ex-             V @ 100° C.                                                                       V @40° C.                                                                           Pour                                  ample HVI-PAO   cS         cS      VI   Point °C.                      ______________________________________                                        LN142 mineral oil                                                                             4.03       20.02    97  -14                                   Exam. 3300 cS   4.15       20.49   103  -16                                   13    1-decene                                                                      HVI-PAO                                                                 Exam. C.sub.6 -C.sub.14                 -16                                   14    α-olefins                                                         Exam. 1-decene &                        -15                                   15    4-methyl-                                                                     1-pentene                                                               Exam. 57 cS     4.06       20.09   100  -14°C.                         16    HVI-PAO                                                                       from 70/30                                                                    C.sub.10 /C.sub.20-24                                                   ______________________________________                                    

A key discovery of the present invention is the fact that the productsof the invention, in order to demonstrate a large pour point depressanteffect must contain a relatively high proportion of higher carbon numberalpha olefins. Optimally, the feed to the oligomerization process shouldcontain a relatively higher proportion of alpha olefins having a carbonnumber of C₁₆ -C₂₀. In this case, the addition of a small quantity ofthe copolymer of the invention to a lubricant base stock will provide asignificant reduction in pour point. Surprisingly, the additive of theinvention, besides contributing pour point lowering of the lubricantfluid, also act as a viscosity index improver (VII) and increases theviscosity index of the lubricant. This effect is achievedsimultaneously, i.e., pore point is depressed while viscosity index ofthe lubricant is increased. Therefore, the products of the invention actas an additive which both reduces a lubricant base stock pour point(PPD) and increases viscosity index (VII).

The following examples 17-22 are presented to illustrate the qualitiesof the product of the invention to lower pour point and to increaseviscosity index. Examples 17-20 are presented to specifically illustratethe effect of various copolymer compositions containing a relativelyhigh proportion of higher carbon number alpha olefins in the feed.Examples 21-22 present the results of experiments showing the ability ofthe products of the invention to simultaneously reduce pore point andincrease viscosity index.

EXAMPLE 17

A copolymer of Mn (number average molecular weight) 8845 and MWD(molecular weight distribution) 3.34 was prepared by reacting anα-olefin mixture containing 1-hexene, 1-hexadecene, 1-octadecene and1-eicosene (46 wt %, 20 wt % and 20%, respectively) over an activatedCr/SiO₂ catalyst. When 0.20 wt % of this polymer was blended with LN142lubricant base stock, the pour point of the base oil was depressed from-14° C. down to -38° C. This example demonstrated that C₁₆ -C₂₀α-olefins are necessary components for good PPD effect.

EXAMPLE 18

A copolymer was prepared as described in Example 17, except the startingolefins contain 1-hexene and 1-octadecene (50 wt % and 50%,respectively). When 0.27 wt % of this polymer, with Mn 11,890 and MWD5.8, was blended with LN142, the pour point was depressed from -14° C.down to -36° C.

EXAMPLE 19

A copolymer was prepared by the process of the invention with Mn of28,630 and MWD of 3.97 from an alpha-olefin mixture containing 70%1-decene and 30% Gulftene C₂₀₋₂₄ α-olefins. When 0.24% of this polymerwas blended with LN142 base stock, the pour point decreased from -14° C.to -36° C.

EXAMPLE 20

A copolymer with Mn 35,220 and MWD 4.32 was prepared from analpha-olefin mixture containing 50% 1-decene, 25% C₂₀₋₂₄ α-olefins(Gulftene 20-24) and 25% C₂₄₋₂₈ α-olefins (Gulftene 24-28). When 0.22%of this polymer was blended with LN142 base stock the pour point wasdepressed to -22° C. from -14° C.

EXAMPLE 21

A mixed HVI-PAO copolymer of the invention was prepared from a mixturecontaining 60% 1-decene and 40% 1-octadecene to provide a copolymerhaving a number averaged MW of 30,100 and MWD (molecular weightdistribution) of 9.02. The copolymer so formed was blended with a 150sus mineral oil, LN 321. and demonstrates that the mixed HVI-PAOcopolymer can function as both a VI improver and a pour point depressantwhen higher concentrations of the mixed HVI-PAO copolymer are blendedwith a mineral oil basestock. The results are summarized in thefollowing Table 6. The results show that when up to 1 weight % mixedHVI-PAO copolymer of the invention was blended with the mineral oil boththe VI and the pour point improved significantly.

EXAMPLE 22

An experiment was carried out similar to Example 21 except the mixedHVI-PAO copolymer was prepared from a mixture of 50% C₆ and 50% C₁₈α-olefins and had a Mn of 11,900 and MWD of 5.8. The base oil used inExample 22 is a 100" mineral oil stock 142. The results are presented inTable 7. As in the previous Example 21, this example demonstrates thatthe mixed HVI-PAO copolymer of the invention improves the pour point andVI of the base stock simultaneously.

                  TABLE 6                                                         ______________________________________                                        Mixed HVI-PAO and Stock LN321 (Example 21)                                    Wt %    V @ 100° C.                                                                              °C. Pour                                     HVI-PAO cS         VI     Point  ΔVI                                                                          Δpour point                       ______________________________________                                        0       4.61       106    -3     --   --                                      0.25    5.19       114    -30     8   27                                      0.48    5.19       118    -37    15   34                                      1.18    5.98       133    -39    27   36                                      ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        Mixed HVI-PAO and LN142 (Example 22)                                          Wt %    V @ 100° C.                                                                              °C. Pour                                     HVI-PAO cS         VI     Point  ΔVI                                                                          Δpour point                       ______________________________________                                        0       4.03       97     -14    --   --                                      0.27    4.18       97     -36     0   22                                      0.67    4.46       111    -38    14   24                                      1.08    4.74       121    -38    24   24                                      ______________________________________                                    

Specifically preferred mixtures of 1-alkene monomers useful asfeedstream for the present invention include: C₆, C₈, C₁₀, C₁₂, C₁₄,C₁₅, C₁₆, C₁₈ and C₂₀ 1-alkenes; C₆ and C₁₈ 1-alkenes; C₁₀ and C₂₀₋₂₄1-alkenes; C₁₀ and C₂₀₋₂₈ 1-alkenes; C₆, C₁₆, C₁₈ and C₂₀ 1-alkenes, andC₁₀ and C₁₈ 1-alkenes.

What is claimed is:
 1. A hydrocarbon lubricant additive suitable as apour point depressant, cloud point depressant and viscosity indeximprover, said additive comprising the copolymer residue of a mixture of1-alkene comonomers selected from the group consisting of C₃ -C₂₈1-alkenes, wherein said copolymer contains at least 10 weight percent ofrecurring monomeric units of C₁₄ -C₂₄ 1-alkenes; has a number averagemolecular weight between 5,000 and 60,000; and a molecular weightdistribution between 1 and 10; said additive containing a bimodaldistribution of said 1-alkenes in said residue, said distribution havinga first maximum between C₃ and C₁₄ 1-alkenes and a second maximumbetween C₁₄ and C₂₆ 1-alkenes.
 2. The additive of claim 1 wherein saidmixture of 1-alkenes comprises a bimodal mixture of C₆ -C₂₄ 1-alkenes.3. The additive of claim 1 comprising the copolymer of 1-decene and or1-Hexene and 1-octadecene.
 4. The additive of claim 3 wherein the moleratio of 1-decene or 1-hexene to 1-octadecene is about 3 to
 2. 5. Ahydrocarbon lubricant mixture having a reduced pour point comprisingpoly(α-olefin) and the pour point depressant of claim
 1. 6. Ahydrocarbon lubricant mixture having a reduced pour point below -30° C.comprising mineral oil and less than 1 weight percent of the pour pointdepressant of claim
 1. 7. The mixture of claim 6 containing between 0.01and 1.0 weight percent of said pour point depressant.
 8. The mixture ofclaim 6 containing about 0.26 weight percent of said depressant.
 9. Theadditive of claim 1 wherein said mixture of 1-alkene comonomerscomprises C₆, C₈, C₁₀, C₁₂, C₁₄, C₁₅, C₁₆, C₁₈ and C₂₀ 1-alkenes. 10.The additive of claim 1 wherein said mixture of 1-alkene comonomerscomprises C₆ and C₁₈ 1-alkenes.
 11. The additive of claim 1 wherein saidmixture of 1-alkene comonomers comprises C₁₀ and C₂₀₋₂₄ 1l -alkenes. 12.The additive of claim 1 wherein said mixture of 1-alkene comonomerscomprises C₁₀ and C₂₀₋₂₈ 1-alkenes.
 13. The additive of claim 1 whereinsaid mixture of 1-alkene comonomers comprises C₆, C₁₆, C₁₈ and C₂₀1-alkenes.
 14. The hydrocarbon mixture of claim 6 wherein said mineraloil is selected from the group consisting of solvent dewaxed mineraloil, catalytic dewaxed mineral oil and solvent dewaxed wax-isomerizedmineral oil.
 15. A near-linear liquid hydrocarbon copolymer useful ininhibiting the low temperature formation of wax particles in liquidhydrocarbon lubricants and fuels, said copolymer comprisingpoly(1-alkene) and containing between 300 and 4500 carbon atoms, whereinrecurring monomeric units of said copolymer comprise a mixture ofolefins selected from the group consisting of ethylene and C₃ and C₂₈1-alkenes and comprise a bimodal distribution of said 1-alkenes in saidrecurring units having a first maximum between C₁₄ and C₂₆ 1-alkenes anda second maximum between C₁₄ and C₂₆ 1-alkenes with at least 10 weightpercent of the pendant chains of said copolymer containing between 12and 22 carbon atoms.
 16. The copolymer of claim 15 wherein saidrecurring units comprise a mixture of C₆ -C₂₄ 1-alkenes.
 17. Thecopolymer of claim 15 comprising the copolymer of 1-decene or 1-hexeneand 1-octadecene.
 18. The copolymer of claim 15 wherein said lubricantcomprises mineral oil or hydroprocessed lubricants.
 19. The copolymer ofclaim 15 wherein said lubricant comprises poly(alphaolefins).
 20. Thecopolymer of claim 15 wherein said fuel comprises diesel fuel.